The many different types and numbers of tapping tools on the market reflect designs in which the designers pursued different goals which are served by the designs. For some goals, the resulting design dictates a device which suffers in other areas. Those other areas can include high cost, lack of ease of use, excessive work space requirements, and other disadvantages.
Setting aside automated, highly specific dedicated machine tappers, as well as other large tapping dedicated devices, the devices which have developed for short run shop tapping have a definite historical progression. In the simplest form, a manual chuck with “T” shaped handles would be used to carefully align with a bore with the user manually using both hands and a sharp eye to both manually align and manually turn the tap.
A further improvement included the inclusion of a pin at the center of the tapping tool so that it could be used with a machine spindle in order to derive alignment. However, beginning the step of turning of the tap with advancement of the tap into the bore either caused the tap to lose its guiding connection with an axially non-moveable spindle, or required some other action by the user in operating a different mechanism to try and move the spindle.
As a variation on this configuration, a guide which provided a close tolerance bore for movement of the pin was attached to the spindle to give alignment, but which allows the advance of the tapping tool with respect to the guide. However, the starting of the tapping process caused the tapping device pin to move down and eventually out of the bore, resulting in loss of alignment.
A further variation is illustrated in U.S. Pat. No. 4,087,195 to James R. Wood, entitled “TAPPING ACCESSORY”, incorporated by reference herein, which utilizes a telescoping sleeve and post arrangement. A rod insert is fixed in a chuck in the same manner as a drill bit would be fixed. The tapping tool has a guide bore which is engaged by the rod insert as the tapping tool is axially moved onto the rod insert and upward toward the chuck.
The shortcomings of this arrangement are several. First, the axial length of the bore in the tapping tool and the insert may prohibit ease of removal of the tapping tool from the insert in order to easily change the tap. Changing the tap with the device of Woods while in place over the insert would involve one hand to lift upwardly on the tapping device while the other hand is used to loosen the tap chuck. A “third hand” is needed to retrieve the tap and load in a new one. As a result the device of Woods either disassembles or requires breaking the work piece setup each time a change of tap is needed.
Second, the device of Wood requires one hand to hold the tapping device upward and clear of the work piece while the work piece is being positioned. If the working table requires two hands to move the work piece into position, a third hand is again needed. Without the upward force on the device of Wood, the tapping device would freely slide down the rod insert and impact or scratch across the work piece.
Third, because of unsteadiness and the need for a third hand in positioning the work piece, the device of Wood naturally causes the user to operate with significant clearance over a work piece to avoid inadvertent contact between the tap and the work piece during pre-tap positioning. This over clearance results in a significant portion of the length of telescoping travel to be utilized as clearance to make up for the ungainliness involved in work piece change. This can cause the premature loss of guidance where the tapping device of Wood begins from a position too far down the rod insert.
Fourth, when the tapping tool of Wood is backed out of the tapped hole, a manual user may have a tendency to spin the tap at its point of departure from the now threaded bore to potentially damage the threads nearest the threaded bore opening.
Fifth, in terms of general use, the device of Wood is a disassembled two piece affair. It has to be disassembled and re-assembled each time it is used. The rod insert is loaded into the drill chuck, followed by loading the tapping tool onto the rod insert, and then holding the tapping tool upwardly in place while having to adjust both the work piece alignment and possibly the height of the drill chuck if it is adjustable. Otherwise, the user must guess the proper height of the drill chuck before the rod insert is loaded.
What is needed is a device which overcomes limitations of the Wood tapping device and which eliminates the need for a third hand to both support a tapping device while positioning the work piece; eliminates the need to guess the proper separation between the work piece and the drill chuck; eliminates the two piece assembly, disassembly and stepwise assembly actions required with a telescoping rod insert free from its associated guide socket; facilitates two handed change of taps without having to disassemble the tapping tool; and prevents inadvertent action at the tap opening upon backing out of the tap from the threaded bore.